The first one is actually a boot label.The boot label is used to determine what boot options are to be used. Look inside a syslinux.cfg, isolinux.cfg, grub's menu.lst or lilo.conf. Many boot lines are specified in each of these. Some are presented on menu, some are referenced by number. Depends on boot loader.

I don't know the boot process half as well as I'd like, but i was under the impression that "dsl" was placed there to delimit the options to be used after the system has taken care of configuring the hardware necessary to run the operating system. These options would be checked by the dsl-config script.Still I'm not completely comfortable with my answer.